Oil and gas geochemical exploration in the southern part of East China Sea Shelf Basin—Hydrocarbon anomalies and integrated evaluation of oil-gas potentials
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摘要: 通过对东海陆架盆地南部海域油气地球化学样品采集、酸解烃类气体和芳烃类指标的分析测试，以及地球化学异常提取，揭示了烃类地球化学指标的异常分布特征，分析了烃类气体的成因类型和深部油气属性，进行了综合地球化学异常分区和含油气性评价。烃类地球化学指标，包括酸解甲烷、酸解乙烷、芳烃及其衍生物总量260 nm和稠环芳烃总量360 nm的异常，主要集中分布在研究区的西部和东部，分别与瓯江凹陷和闽江凹陷相对应。酸解烃类气体组合及甲烷碳同位素组成指示酸解烃类气体异常主要为热成因并遭受了表层氧化，深部油气属性属于干气至凝析油气，以干气为主。根据综合地球化学异常特征，划分了西部综合地球化学异常区和东部综合地球化学异常区。酸解甲烷、酸解乙烷、芳烃及其衍生物总量260 nm和稠环芳烃总量360 nm指标异常在西部综合地球化学异常区均有明显显示，而东部综合地球化学异常区则以酸解烃类气体异常为主，稠环芳烃总量360 nm异常部分分布，芳烃及其衍生物总量260 nm异常只有零星分布。综合评价结果表明，西部综合地球化学异常区含油气性明显优于东部综合地球化学异常区，也就是瓯江凹陷的含油气性好于闽江凹陷。Abstract: Geochemical samples are collected from the southern part of East China Sea Shelf Basin and analyzed for oil and gas geochemical indices by the authors. Geochemical indices, such as acidolysis hydrocarbon gases and aromatic hydrocarbons are analyzed. From the analysis results, geochemical anomalies are extracted, and the distribution patterns of anomalous hydrocarbon geochemical indicators revealed, in addition to the genetic types of hydrocarbon gases and deep hydrocarbon attributes. Based upon the work, integrated geochemical anomaly areas are defined and their hydrocarbon-bearing capacity evaluated for the southern area of the East China Sea Shelf Basin. The indicators of the hydrocarbon geochemical anomalies include acidolysis methane and acidolysis ethane. The anomalies with total aromatics and their derivatives over 260 nm and the total polycyclic aromatic hydrocarbons above 360 nm, are mainly distributed in the eastern and western parts of the study area, corresponding to the Oujiang Sag and Minjiang Sag, respectively. Acidolysis hydrocarbon gas assemblages and methane carbon isotope compositions suggest that the anomalies of acidolysis hydrocarbon gas are mainly thermogenic type and have suffered surface oxidation. Deep hydrocarbon attributes suggest a source of dry gas to condensate oil -gas, dominated by dry gas. According to the distribution pattern of geochemical anomalies, the western comprehensive geochemical anomaly area and the eastern comprehensive geochemical anomaly areas are divided. The anomalies of acidolysis methane, acidolysis ethane, total aromatics and their derivatives over 260 nm and total polycyclic aromatics over 360 nm are evident in the western comprehensive geochemical anomaly area, while the eastern comprehensive geochemical anomaly area is dominated by acidolysis hydrocarbon gas anomalies. The total polycyclic aromatics at 360 nm are locally observed, the total aromatics and their derivatives at 260 nm are only sporadically observed in the east comprehensive geochemical anomaly area. Therefore, the western comprehensive geochemical anomaly area is obviously better than that of the eastern comprehensive geochemical anomaly area, that is, the oil and gas-bearing capacity of the Oujiang Sag is better than that of the Minjiang Sag.
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图 1 东海陆架盆地南部海域地球化学探测取样站位图
Figure 1. Sampling locations of geochemical exploration in the southern part of the East China Sea Shelf Basin
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图 4 海底沉积物酸解甲烷地球化学异常分布图
Figure 4. Geochemical anomaly map of acidolysis methane from seabed sediments
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图 5 海底沉积物酸解乙烷地球化学异常分布图
Figure 5. Geochemical anomaly map of acidolysis ethane from seabed sediments
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图 6 海底沉积物芳烃及其衍生物总量260 nm地球化学异常分布图
Figure 6. Geochemical anomaly map of the total amount of aromatics and their derivatives over 260 nm from seabed sediments
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图 7 海底沉积物稠环芳烃总量360 nm地球化学异常分布图
Figure 7. Geochemical anomaly map of the total amount of polycyclic aromatic hydrocarbons over 360 nm from seabed sediments
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图 12 东海陆架盆地南部海域油气地球化学异常区综合评价
Figure 12. Comprehensive evaluation map of oil and gas geochemical anomaly areas in the southern part of the East China Sea Shelf Basin
表 1 地球化学指标数值特征
Table 1 Data of geochemical indicators
指标及数值参数 最小值 最大值 均值 标准偏差 变异系数 酸解甲烷(μL/kg) 28.34 1 106.38 310.13 181.71 0.59 酸解乙烷(μL/kg) 0.62 16.95 5.91 3.32 0.56 酸解丙烷(μL/kg) 0.15 4.63 1.76 0.93 0.53 酸解异丁烷(μL/kg) 0.03 1.15 0.47 0.26 0.55 酸解正丁烷(μL/kg) 0.04 1.53 0.57 0.32 0.56 酸解异戊烷(μL/kg) 0.05 0.97 0.34 0.21 0.62 酸解正戊烷(μL/kg) 0.02 0.67 0.23 0.13 0.57 芳烃及其衍生物220 nm(ω(B)(10−9)) 2.90 2 615.70 218.47 489.21 2.24 芳烃及其衍生物260 nm(ω(B)(10−9)) 1.00 2 502.10 154.82 404.14 2.61 芳烃及其衍生物275 nm(ω(B)(10−9)) 0.60 2 520.60 149.97 400.90 2.67 稠环芳烃320 nm(ω(B)(10−9)) 5.90 75.00 18.61 7.87 0.43 稠环芳烃360 nm(ω(B)(10−9)) 6.40 79.00 21.59 12.44 0.58 稠环芳烃405 nm(ω(B)(10−9)) 1.20 46.00 7.01 6.46 0.92 
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Table 2 Discriminant index of anomaly attributes of acidolysis hydrocarbon gases from seabed sediments[7-8]
C1/C2+C3 C1/C2 δ13C1/‰ 判别标准 生物构成 ＞1 000 ＜−54 热成因 ＜50 4～100 −20～−54 研究区酸解烃类气体 29.80～54.98 39.78～72.07 −32.4～−34.8
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表 3 东海陆架盆地南部海域综合地球化学异常区累积得分及评价结果
Table 3 Accumulative score and evaluation results of comprehensive geochemical areas in the southern part of the East China Sea shelf basin
综合地球化学异常区 评价因子 异常指标 累积得分 酸解甲烷 酸解乙烷 芳烃及其衍生物总量260 nm 稠环芳烃总量360 nm 西部综合地球化学异常区（A） 异常规模 2 2 2 2 25 异常强度 2 2 2 2 构造符合 2 2 2 2 油气显示 1 东部综合地球化学异常区（B） 异常规模 2 2 0 1 15 异常强度 2 2 0 1 构造符合 2 2 0 1 油气显示 0
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